The tenth cranial nerve, the vagus, is distributed throughout the body, including major divisions to all parts of the gut, and to the liver. This cholinergic nerve restrains inflammation, in all the organs to which the vagus is distributed, by the tonic release of acetylcholine (ACh) onto nicotinic receptors (nicAChRs) of the alpha7- subtype. In addition to their presence on inflammatory cells, alpha7-nicAChRs are also present on cell bodies of the vagus in the CNS, where they cause vagal activation and neuroprotection. Since the presence of alcohol inhibits alpha7-nicAChRs, and a known chronic effect is to cause vagal neuropathy, these anti-inflammatory effects of the vagus are seriously compromised during alcohol exposure. The primary hypothesis is that this reduced vagal function contributes to the chronic inflammation following oxidative stress, which is a common feature of alcohol-induced damage in many organs. If correct, this predicts that compounds with alpha7- nicAChR agonist properties will protect against alcohol-induced tissue damage, particularly if these compounds are also anti-oxidants. The first specific aim of this proposal is to test the primary hypothesis in vitro by studying the interactions of alcohol and alpha7-nicAChR ligands on endotoxin-induced release of mediators from inflammatory cells (splenic, lung and peritoneal macrophages) from wild-type, and alpha7-nicAChR knock-out, C57Bl/6J mice. The second specific aim is to test the hypothesis in vivo by exposing C57Bl/6J mice (wild-type, vagotomized, and alpha7-nicAChR knockouts) chronically to alcohol by forced consumption, and then evaluating endotoxin-induced release of inflammatory mediators in vivo. As part of these studies we will evaluate the therapeutic potential of the alpha7-nicAChR agonist, choline, and a methylquercetagetin which acts as a partial agonist at alpha7-nicAChRs. The latter was recently discovered by screening a native plant extract library, and has potent anti-oxidant activity in addition to its action at nicAChRs, where it has an affinity comparable to choline. The ability of these compounds to inhibit endotoxin-induced release of inflammatory mediators following alcohol exposure will be studied in vitro and in vivo using the same methods as above. This project therefore tests a novel hypothesis for alcohol-induced organ damage based on the interaction between brain, gut and liver as represented by the vagus nerve, and tests a novel therapeutic approach to this.
Alcoholism (either dependence or abuse) affects more than 8% of the population of the US, and the societal costs approach $200BN annually. About half of this sum is medical cost, much of which is accrued in treating alcohol-related organ damage. Despite this there are currently no accepted approaches to preventing or reversing this damage. This application proposes a novel hypothesis as to the cause of organ damage which has profound implications for treatment. If successful, the project will establish a framework for drug discovery and evaluation in relation to this largely overlooked therapeutic target.
|Lutz, Joseph A; Kulshrestha, Manish; Rogers, Dennis T et al. (2014) A nicotinic receptor-mediated anti-inflammatory effect of the flavonoid rhamnetin in BV2 microglia. Fitoterapia 98:11-21|